test: redesign 6 skipped/todo E2E tests + add test.concurrent support

Redesigned tests (previously skipped/todo):
- contributor-mode: pre-fail approach, 5 turns/30s (was 10 turns/90s)
- design-consultation-research: WebSearch-only, 8 turns/90s (was 45/480s)
- design-consultation-preview: preview HTML only, 8 turns/90s (was 30/480s)
- qa-bootstrap: bootstrap-only, 12 turns/90s (was 65/420s)
- /ship workflow: local bare remote, 15 turns/120s (was test.todo)
- /setup-browser-cookies: browser detection smoke, 5 turns/45s (was test.todo)

Added testConcurrentIfSelected() helper for future parallelization.
Updated touchfiles entries for all 6 re-enabled tests.

Target: 0 skip, 0 todo, 0 fail across all E2E tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/touchfiles.test.ts

@@ -132,7 +132,7 @@ describe('selectTests', () => {
     const result = selectTests(['SKILL.md.tmpl'], E2E_TOUCHFILES);
     // Should select the 7 tests that depend on root SKILL.md
     expect(result.selected).toContain('skillmd-setup-discovery');
-    // contributor-mode is now skipped — not in E2E_TOUCHFILES
+    expect(result.selected).toContain('contributor-mode');
     expect(result.selected).toContain('session-awareness');
     // Also selects journey routing tests (SKILL.md.tmpl in their touchfiles)
     expect(result.selected).toContain('journey-ideation');